Floating dry dock



Feb. 24. '1 925. 1,527,546

G. C. ENGSTRAND I FLOATING DRY DOCK Filed. May a; 1922 F/Q. E.

Patented Feb. 24, 1925.

1,527,546 PATE3N-17OFF56E;

GUNNAR C. ENGSTRAND, 013 BROOKLYN, NEVT YORK.

rnorrrrne Applicationfiled May a,

To all whomit may concern:

Be it known that T, GUNNAR C. ENG srnann, a subject of the King of Sweden. residin g at Brooklyn, in the county of Kings and Eltateof New York, have invented certain new and useful lmprovements in Floating Dry lDocks, of which the following is a specification.

My invention has for its object to furnish a floating dry dock pontoon, the cross sec tion of which is massed towards the center and below the jshipin order to reduce the bending stresses due to the central ship load.

lidy invention hasalso tor its object to provide a floating dry dock pontoon of rectilinear cross section which is narrower at the bottom than at the deck. The free water surface insidesuch a pontoon willgradually contract as the pumping out process pro ceeds, and the dock is thus rendered more stable for an increased ship load.

My invention has for a further object to provide double flanged deck stringers which at the center of the pontoon are di-- agonally braced to the double flanged bottom stringers, the ends of which are bent upwards and secured to the ends of the deck stringers thus forming triangular end truss elements.

My invention has for a further object to provide diagonally braced trusses adapt ed to transmit bendingstresses alteri'iating with frames adapted to withstand pressure loads only.

My invention has for a still further ob ject to provide a series of pontoons attached at each end to continuous side walls or wings by means of bolts which pass bodily through the ends of the pontoons and are entirely above the water when the dock is pumped out light.

In the drawings :Figure 1 is a combined cross section of the dry dock, showing the diagonally braced trusses and the pressure frames. In the figure a ship is shown raised clear out of the water, which still covers the pontoon deck of the dock.

Figure 2 shows a longitudinal elevation and section combined of the dock which is shown pumped out light.

Referring to the drawings, in which like reference characters designate corresponding parts, 1 designates the floating dry dock comprising a series of pontoons 2, which are at their ends attached to the continuhas: been.

1922. iSerial No. 559,452.

ous side walls or wings 3by means of brackets 17 and through bolts 18 which pass through the timbers 10 and 1.4;.

In the pontoon 2 the composite trusses 4 alternate with the pressure frames The composite truss t comprises the double flanged deck stringers 6 and bottom stringers 7 which are clamped to the uprights of the center bulkhead 11. and the intermediate bulkheads 13. The center bulkhead 11 is watertight and tight fitting chocks 12 are fitted between the stringers. The deck stringers 6 are at the center of the dock braced to the bottom stringers 7 by means of the diagonal tension members 8 over the longitiu'linal bulkheads 11 and 13 and the bottom stringers 7 at their ends are bent upwards andsecured to the deck stringers 6 by means of the flanged plates 9 to which the side logs 10 are secured.

The pressure frame 5 comprises deck stringers 23 and the bottom stringers are made up of the central members 15 to which the end members 16 are attached so as to conform with the outline of the composite trusst. The end members 16 are also secured to the ends of the deckstringers 23 in a conventional manner.

A ship 21 is shown properly blocked in the dock 1 and the outside water line 19 indicatesthat the ship has just been raised clear out of the water;

The inside water linesQO and 22 indicate the height of water inside the pontoon.

The water line 2 1 in Figure 2 indicates the draft of the dock when pumped out light without any ship.

It is evident that when the pontoons 2 support the maximum ship which the dock can handle, the deck of the pontoons will just be awash.

lit is also evident that the maximum ship will cause the maximum strain in the pontoon truss, and the pontoon truss has to he designed to withstand such a maximum load.

It is also evident that in the trapezoid shaped pontoon the deck and bottom stringers are less strained than in the conventional rectangular pontoon of equal capacity, as the upwards acting buoyancy load at the end of the truss has been materiallyreduced.

When a ship is docked and is ust clearing the water, the entire stability is due to the side walls or wings 3.

The wings 3 have to balance the upsetting moment due to the elevated weight of the ship and also the upsetting moment due to the inside free water surfaces 20 and 22 in the pontoons 2.

It is evident that in the trapezoid shaped pontoon 2, the upsetting moment due to the inside free water surfaces in the pontoon grows less the more the pontoon is pumped out, while this moment is constant in the conventional rectangular pontoon.

In the trapezoid shaped pontoon, the upsetting moment of the tree bilge water is tnus reduced to a n'iinimum when the ship load a maximum, and the width of the wings required for the conventional dry dock can be materially reduced in the shown type oi do k.

it is evident that the pressure frames 5 are not adapted to transl'nit bending stresses due to the central shipload as they are not diagonally braced. The intermediate bulkheads 13 carry the stresses over to the composite trusses 4, which are diagonally braced.

The reduction of the displacement oi? the poutoons at the ends reduces the bending stresses to such an extent that diagonal bracing only necessary in every second frame, the required frame spacing being determined by the water pressure.

It is readily seen from Figure 2 in the drawing that the bolts 18 are entirely above the light load water line 24 ot the dock and consequently the bolts are readily removed and replaced from the outside of the dock.

I do not desire to be understood as limiting myself to the specific details of construction and arrangement as herein described and illustrated, as it is manifest that *ariations and modifications may be made in. the adaptation of the device to various conditions, without departing from the spirit and scope of my invention.

I claim 1. In a floating dry dock, buoyant side "alls or wings, entirely submersible pontoons of a rectilinear and trapezoid cross section having transverse deck and bottom stringers parallel and diagonally braced together at the center, the ends of the bottom stringers being bent upwards at points located well inside the wings and secured to the ends of the deck stringers, thus forming triangular end truss elements which support besides the side walls or wings the unloaded working deck between the ship sides and the wings.

2. In a floating dry dock, an entirely sub- IHQI'SllDlG- pontoon part of trapezoid cross section adapted to support elevated and central ship loads and extending for the entire length of the dock, said pontoon part having stability means comprising in combination buoyant wings also extending for the entire length of the dock and rigidly attached to the ends of said pontoon part and a watertight center bulkhead dividing the pontoon part laterally in two pumping compartments with their outer and inner walls converging towards the bottom so as to gradually reduce the free inside water surfaces during pumping.

3. In a floating trapezoid shaped dry dock pontoon, trusses having deck and bottom stringers diagonally braced together over longitudinal bulkheads, said trusses alternating with pressure frames without such bracing, said frames conforming with the outline 01" the trusses and supported by the longitudinal bulkheads, substantially as described.

GUNNAR C. ENGSTRAND. itnesses FRANK Nronons, FRANK MCCOLLOUGH. 

